The effect of cutting turn on the content of prussic acid and nitrate in forage sorghum

In the sorghum plant, prussic acid and nitrate are the main anti-nutritional compounds that can harm animals if the permitted levels are exceeded. This study aimed to determine the effect of cutting sequentially on prussic acid and nitrate content in eighteen varieties of sorghum forage including four Iranian domestic and fourteen imported varieties. All varieties under the same irrigation, fertilization, light, and temperature conditions were planted. The first and second cuttings were conducted at the flowering stage, and 50 days later, respectively. According to the results, the foreign variety of FS one BMR had the highest amount of prussic acid in both cuttings but this compound level reduced from 481 ppm in the first cutting to 397 ppm in the second one. While the lowest content of prussic acid was detected in the Titan variety (163 and 37 ppm in the first and second cuttings, respectively). In the second cutting, nitrate contents were also significantly lower than those in the first one. Moreover, two varieties of Juicy sweet 2 and Juicy Sweet BMR SSH.1 recorded the maximum nitrate content (2417, and 2089 ppm, respectively) in the first cutting. By contrast, the minimum nitrate found in KFS-2 and FGCSI09 varieties by 127 and 143 ppm, respectively at the same time. Regarding the second harvesting, HFS1 and PFS-21 varieties recorded the highest nitrate content (162 and 150 ppm, respectively) whereas FGCSI12 and PHFS-27 varieties had the minimum amounts of 14 and 64 ppm, respectively. As compared with the recommended tolerable levels of prussic acid and nitrate in animal feed, the  studied varieties were not toxic in the first cutting, and both compounds decreased significantly in the second cutting.